I n t e r n a t i o n a l

T e l e c o m m u n i c a t i o n

U n i o n

ITU-TTELECOMMUNICATION STANDARDIZATION SECTOR OF ITU

H.248.1(09/2005)

SERIES H: AUDIOVISUAL AND MULTIMEDIA SYSTEMS Infrastructure of audiovisual services Communication procedures

Gateway control protocol: Version 3

ITU-T Recommendation H.248.1

ITU-T H-SERIES RECOMMENDATIONS AUDIOVISUAL AND MULTIMEDIA SYSTEMS CHARACTERISTICS OF VISUAL TELEPHONE SYSTEMS INFRASTRUCTURE OF AUDIOVISUAL SERVICES General Transmission multiplexing and synchronization Systems aspects Communication procedures Coding of moving video Related systems aspects Systems and terminal equipment for audiovisual services Directory services architecture for audiovisual and multimedia services Quality of service architecture for audiovisual and multimedia services Supplementary services for multimedia MOBILITY AND COLLABORATION PROCEDURES Overview of Mobility and Collaboration, definitions, protocols and procedures Mobility for H-Series multimedia systems and services Mobile multimedia collaboration applications and services Security for mobile multimedia systems and services Security for mobile multimedia collaboration applications and services Mobility interworking procedures Mobile multimedia collaboration inter-working procedures BROADBAND AND TRIPLE-PLAY MULTIMEDIA SERVICES Broadband multimedia services over VDSLFor further details, please refer to the list of ITU-T Recommendations.

H.100H.199 H.200H.219 H.220H.229 H.230H.239 H.240H.259 H.260H.279 H.280H.299 H.300H.349 H.350H.359 H.360H.369 H.450H.499 H.500H.509 H.510H.519 H.520H.529 H.530H.539 H.540H.549 H.550H.559 H.560H.569 H.610H.619

ITU-T Recommendation H.248.1 Gateway control protocol: Version 3

Summary To achieve greater scalability, this Recommendation decomposes the H.323 Gateway function defined in ITU-T Rec. H.246 into functional subcomponents and specifies the protocols these components use to communicate. This allows implementations of H.323 gateways to be highly scalable and encourages leverage of widely deployed Switched Circuit Network (SCN) capabilities such as SS7 switches. This also enables H.323 gateways to be composed of components from multiple vendors distributed across multiple physical platforms. The purpose of this Recommendation is to add capabilities currently defined for H.323 systems and is intended to provide new ways of performing operations already supported in H.323. This Recommendation includes several enhancements to ITU-T Rec. H.248.1 Version 2: capability to define context properties via packages; an IEPS context property; a flag to indicate that the MG has OutOfService terminations to report at registration time; new message segmentation package and procedures for non-segmenting transports; refined package definition requirements and a new package template; refined profile definition requirements and a new profile template; addition of statistics on a stream level; addition of a signal request identifier to differentiate similar signals within a SignalList; addition of a base signal parameter to indicate in which direction to play the signal; addition of two new Topology types; addition of an intersignal delay timer for signals in a SignalList; addition of a new ContextIDList construct for command responses; addition of a TerminationIDList construct for commands and responses; refined ServiceChange procedures; addition of a capability for the MGC to regulate the rate at which it receives notifications; addition of the ability to add filter conditions to audit requests.

Source ITU-T Recommendation H.248.1 was approved on 13 September 2005 by ITU-T Study Group 16 (2005-2008) under the ITU-T Recommendation A.8 procedure.

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FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.

NOTE In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.

INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database.

ITU 2006 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.

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CONTENTS Page 1 2 Scope ............................................................................................................................ References..................................................................................................................... 2.1 Normative references...................................................................................... 2.2 Informative references.................................................................................... Definitions .................................................................................................................... Abbreviations................................................................................................................ Conventions .................................................................................................................. Connection model......................................................................................................... 6.1 Contexts.......................................................................................................... 6.2 Terminations................................................................................................... 6.3 Wildcarding principles ................................................................................... Commands .................................................................................................................... 7.1 Descriptors...................................................................................................... 7.2 Command application programming interface............................................... Transactions.................................................................................................................. 8.1 Common parameters....................................................................................... 8.2 Transaction application programming interface............................................. 8.3 Messages......................................................................................................... Transport....................................................................................................................... 9.1 Ordering of commands ................................................................................... 9.2 Protection against restart avalanche ............................................................... 9.3 Protection against Notify avalanche............................................................... Security considerations................................................................................................. 10.1 Protection of protocol connections................................................................. 10.2 Interim AH scheme......................................................................................... 10.3 Protection of media connections .................................................................... MG-MGC control interface .......................................................................................... 11.1 Multiple Virtual MGs ..................................................................................... 11.2 Cold start ........................................................................................................ 11.3 Negotiation of protocol version...................................................................... 11.4 Failure of a MG .............................................................................................. 11.5 Failure of an MGC.......................................................................................... 11.6 MGC-MG control association monitoring ..................................................... Package definition ........................................................................................................ 12.1 Guidelines for defining packages ................................................................... 12.2 Guidelines to defining parameters to events and signals................................ 12.3 Identifiers........................................................................................................ 1 1 1 3 4 5 6 6 7 8 14 16 16 37 52 54 54 56 57 57 58 59 59 59 59 60 60 60 61 61 62 62 63 63 64 67 68

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Package registration........................................................................................

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Profile definition........................................................................................................... IANA considerations .................................................................................................... 14.1 Packages ......................................................................................................... 14.2 Error codes...................................................................................................... 14.3 ServiceChange reasons................................................................................... 14.4 Profiles............................................................................................................

Annex A Binary encoding of the protocol ............................................................................ A.1 Coding of wildcards ....................................................................................... A.2 ASN.1 syntax specification ............................................................................ A.3 DigitMaps and path names ............................................................................. Annex B Text encoding of the protocol................................................................................ B.1 Coding of wildcards ....................................................................................... B.2 ABNF specification ........................................................................................ B.3 Hexadecimal octet coding .............................................................................. B.4 Hexadecimal octet sequence........................................................................... Annex C Tags for media stream properties .......................................................................... C.1 General media attributes................................................................................. C.2 Mux properties................................................................................................ C.3 General bearer properties ............................................................................... C.4 General ATM properties................................................................................. C.5 Frame relay..................................................................................................... C.6 IP..................................................................................................................... C.7 ATM AAL 2 ................................................................................................... C.8 ATM AAL 1 ................................................................................................... C.9 Bearer capabilities .......................................................................................... C.10 AAL 5 properties............................................................................................ C.11 SDP equivalents.............................................................................................. C.12 H.245 .............................................................................................................. Annex D Transport over IP................................................................................................... D.1 Transport over IP/UDP using Application Level Framing (ALF) ................. D.2 Using TCP ...................................................................................................... Annex E Basic packages ....................................................................................................... E.1 Generic ........................................................................................................... E.2 Base Root Package ......................................................................................... E.3 Tone Generator Package................................................................................. E.4 Tone Detection Package ................................................................................. E.5 Basic DTMF Generator Package.................................................................... E.6 DTMF Detection Package ..............................................................................iv ITU-T Rec. H.248.1 (09/2005)

E.7 E.8 E.9 E.10 E.11 E.12 E.13 E.14 E.15

Call Progress Tones Generator Package......................................................... Call progress tones detection package............................................................ Analog Line Supervision Package.................................................................. Basic Continuity Package............................................................................... Network Package............................................................................................ RTP Package .................................................................................................. TDM Circuit Package..................................................................................... Segmentation Package.................................................................................... Notification Behaviour ...................................................................................

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Annex F ServiceChange Procedures..................................................................................... F.1 Introduction .................................................................................................... F.2 Control Association Definition....................................................................... F.3 Events leading to ServiceChange Procedures ................................................ F.4 ServiceChange Element Description.............................................................. F.5 Use of ServiceChange parameters.................................................................. F.6 ServiceChange versus TerminationState........................................................ Appendix I Example call flows............................................................................................. I.1 Residential gateway to residential gateway call............................................. Appendix II H.248 Package template ................................................................................... Appendix III H.248 Profile Definition template...................................................................

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ITU-T Recommendation H.248.1 Gateway control protocol: Version 31 Scope

This Recommendation defines the protocols used between elements of a physically decomposed multimedia gateway. There are no functional differences from a system view between a decomposed gateway, with distributed sub-components potentially on more than one physical device, and a monolithic gateway such as described in ITU-T Rec. H.246. This Recommendation does not define how gateways, multipoint control units or interactive voice response units (IVRs) work. Instead it creates a general framework that is suitable for these applications. Packet network interfaces may include IP, ATM or possibly others. The interfaces will support a variety of Switched Circuit Network (SCN) signalling systems, including tone signalling, ISDN, ISUP, QSIG and GSM. National variants of these signalling systems will be supported where applicable. Products claiming compliance with Version 1 of ITU-T Rec. H.248.1 shall comply with all of the mandatory requirements of ITU-T Rec. H.248.1 originally approved in 06/2000 and reissued in 03/2002. Products claiming compliance with Version 2 of ITU-T Rec. H.248.1 shall comply with all of the mandatory requirements of ITU-T Rec. H.248.1 originally approved in 05/2002 and updated in 03/2004. Products claiming compliance with this Recommendation shall comply with all of the mandatory requirements of ITU-T Rec. H.248.1 approved on 09/2005. Products shall indicate the version of the protocol in use by using ServiceChangeVersion as '1' to refer to ITU-T Rec. H.248.1 (03/2002), '2' to refer to ITU-T Rec. H.248.1 Corrigendum 1 (03/2004) and '3' to refer to ITU-T Rec. H.248.1 (09/2005). 2 References

The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. 2.1 Normative references ITU-T Recommendation E.106 (2003), International Emergency Preference Scheme (IEPS) for disaster relief operations. ITU-T Recommendation H.225.0 (2003), Call signalling protocols and media stream packetization for packet-based multimedia communication systems. ITU-T Recommendation H.235.0 (2005), H.323 Security: Framework for security in H-series (H.323 and other H.245-based) multimedia systems. ITU-T Recommendation H.245 (2005), Control protocol for multimedia communication. ITU-T Recommendation H.246 (1998), Interworking of H-series multimedia terminals with H-series multimedia terminals and voice/voiceband terminals on GSTN and ISDN.ITU-T Rec. H.248.1 (09/2005) 1

ITU-T Recommendation H.248.4 (2000), Gateway control protocol: Transport over Stream Control Transmission Protocol (SCTP), plus Corrigendum 1 (2004). ITU-T Recommendation H.248.5 (2000), Gateway control protocol: Transport over ATM. ITU-T Recommendation H.248.8 (2005), Gateway control protocol: Error code and service change reason description. ITU-T Recommendation H.248.14 (2002), Gateway control protocol: Inactivity timer package. ITU-T Recommendation H.323 (2003), Packet-based multimedia communications systems. ITU-T Recommendation I.363.1 (1996), B-ISDN ATM Adaptation Layer specification: Type 1 AAL. ITU-T Recommendation I.363.2 (2000), B-ISDN ATM Adaptation Layer specification: Type 2 AAL. ITU-T Recommendation I.363.5 (1996), B-ISDN ATM Adaptation Layer specification: Type 5 AAL. ITU-T Recommendation I.366.1 (1998), Segmentation and Reassembly Service Specific Convergence Sublayer for the AAL type 2. ITU-T Recommendation I.366.2 (2000), AAL type 2 service specific convergence sublayer for narrow-band services, plus Corrigendum 1 (2002). ITU-T Recommendation I.371 (2004), Traffic control and congestion control in B-ISDN. ITU-T Recommendation Q.763 (1999), Signalling System No. 7 ISDN user part formats and codes, plus Amendment 3 (2004). ITU-T Recommendation Q.765.5 (2004), Signalling System No. 7 Application transport mechanism: Bearer Independent Call Control (BICC). ITU-T Recommendation Q.931 (1998), ISDN user-network interface layer 3 specification for basic call control, plus Amendment 1 (2002): Extensions for the support of digital multiplexing equipment. ITU-T Recommendation Q.2630.1 (1999), AAL type 2 signalling protocol Capability Set 1. ITU-T Recommendation Q.2931 (1995), Digital subscriber signalling system No. 2 User-Network Interface (UNI) layer 3 specification for basic call/connection control, plus Amendment 4 (1999). ITU-T Recommendation Q.2941.1 (1997), Digital subscriber signalling system No. 2 Generic identifier transport. ITU-T Recommendation Q.2961.1 (1995), Digital subscriber signalling system No. 2 Additional traffic parameters: Additional signalling capabilities to support traffic parameters for the tagging option and the sustainable call rate parameter set. ITU-T Recommendation Q.2961.2 (1997), Digital subscriber signalling system No. 2 Additional traffic parameters: Support of ATM transfer capability in the broadband bearer capability information element, plus Corrigendum 1 (1999). ITU-T Recommendation Q.2965.1 (1999), Digital subscriber signalling system No. 2 Support of Quality of Service classes, plus Amendment 1 (2000).

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ITU-T Recommendation Q.2965.2 (1999), Digital subscriber signalling system No. 2 Signalling of individual Quality of Service parameters. ITU-T Recommendation V.76 (1996), Generic multiplexer using V.42 LAPM-based procedures, plus Corrigendum 1 (2005). ITU-T Recommendation X.213 (2001) | ISO/IEC 8348:2002, Information technology Open Systems Interconnection Network service definition. ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-1:2002, Information technology Abstract Syntax Notation One (ASN.1): Specification of basic notation, plus Amendment 2 (2004): Alignment with changes made to Rec. X.660 | ISO/IEC 9834-1 for identifiers in object identifier value notation. ITU-T Recommendation X.690 (2002) | ISO/IEC 8825-1:2002, Information Technology ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER), plus Amendment 1 (2003): Support for EXTENDED-XER. ISO/IEC 10646 (2003), Information technology Universal Multiple-Octet Coded character Set (UCS). ATM Forum (1996), ATM User-Network Interface (UNI) Signalling Specification Version 4.0. IETF RFC 1006 (1987), ISO Transport Service on top of the TCP, Version 3. IETF RFC 2234 (1997), Augmented BNF for Syntax Specifications: ABNF. IETF RFC 2327 (1998), SDP: Session Description Protocol. IETF RFC 2402 (1998), IP Authentication Header. IETF RFC 2406 (1998), IP Encapsulating Security Payload (ESP). Informative references ITU-T Recommendation E.180/Q.35 (1998), Technical characteristics of tones for the telephone service. ITU-T Recommendation G.711 (1988), Pulse code modulation (PCM) of voice frequencies. ITU-T Recommendation H.221 (2004), Frame structure for a 64 to 1920 kbit/s channel in audiovisual teleservices. ITU-T Recommendation H.223 (2001), Multiplexing protocol for low bit rate multimedia communication. ITU-T Recommendation H.226 (1998), Channel aggregation protocol for multilink operation on circuit-switched networks. ITU-T Recommendation Q.724 (1998), Telephone user part signalling procedures, plus Amendment 1 (1993). ITU-T Recommendation Q.764 (1999), Signalling System No. 7 ISDN user part signalling procedures, plus Amendment 3 (2004). ITU-T Recommendation Q.1902.4 (2001), Bearer Independent Call Control protocol (Capability Set 2): Basic call procedures, plus Amendment 2 (2004). IETF RFC 768 (1980), User Datagram Protocol. IETF RFC 791 (1981), Internet protocol.ITU-T Rec. H.248.1 (09/2005) 3

2.2

IETF RFC 793 (1981), Transmission control protocol. IETF RFC 1661 (1994), The Point-to-Point Protocol (PPP). IETF RFC 2401 (1998), Security Architecture for the Internet Protocol. IETF RFC 2460 (1998), Internet Protocol, Version 6 (IPv6) Specification. IETF RFC 2805 (2000), Media Gateway Control Protocol Architecture and Requirements. IETF RFC 3261 (2002), SIP: Session Initiation Protocol. IETF RFC 3550 (2003), RTP: A Transport Protocol for Real-Time Applications. IETF RFC 3551 (2003), RTP Profile for Audio and Video Conferences with Minimal Control. Definitions

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This Recommendation defines the following terms: 3.1 access gateway: A type of gateway that provides a User-Network Interface (UNI) such as ISDN. 3.2 descriptor: A syntactic element of the protocol that groups related properties. For instance, the properties of a media flow on the MG can be set by the MGC by including the appropriate descriptor in a command. 3.3 Media Gateway (MG): The media gateway converts media provided in one type of network to the format required in another type of network. For example, a MG could terminate bearer channels from a switched circuit network (e.g., DS0s) and media streams from a packet network (e.g., RTP streams in an IP network). This gateway may be capable of processing audio, video and T.120 alone or in any combination, and will be capable of full duplex media translations. The MG may also play audio/video messages and perform other IVR functions, or may perform media conferencing. 3.4 Media Gateway Controller (MGC): Controls the parts of the call state that pertain to connection control for media channels in a MG. 3.5 Multipoint Control Unit (MCU): An entity that controls the setup and coordination of a multi-user conference that typically includes processing of audio, video and data. 3.6 residential gateway: A gateway that interworks an analogue line to a packet network. A residential gateway typically contains one or two analogue lines and is located at the customer premises. 3.7 SCN FAS signalling gateway: This function contains the SCN Signalling Interface that terminates SS7, ISDN or other signalling links where the call control channel and bearer channels are collocated in the same physical span. 3.8 SCN NFAS signalling gateway: This function contains the SCN Signalling Interface that terminates SS7 or other signalling links where the call control channels are separated from bearer channels. 3.9 stream: Bidirectional media or control flow received/sent by a media gateway as part of a call or conference. 3.10 trunk: A communication channel between two switching systems such as a DS0 on a T1 or E1 line. 3.11 trunking gateway: A gateway between SCN network and packet network that typically terminates a large number of digital circuits.

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4 AAD AAL ADEV ALF ATM C CAS DNS DTMF FAS GSM GW IANA ICANN IEPS IP IS ISUP IVR MG MGC MWD NFAS OoS PRI PSTN QoS RTP SC SCN SG SS7 T, Term

Abbreviations Average Acknowledgement Delay ATM Adaptation Layer Average Deviation Application Level Framing Asynchronous Transfer Mode Context Channel Associated Signalling Domain Name System Dual Tone Multi-Frequency Facility Associated Signalling Global System for Mobile communications Gateway Internet Assigned Numbers Authority (superseded by ICANN) Internet Corporation for Assigned Names and Numbers International Emergency Preference Scheme Internet Protocol In-Service ISDN User Part Interactive Voice Response Media Gateway Media Gateway Controller Maximum Waiting Delay Non-Facility Associated Signalling Out-of-Service Primary Rate Interface Public Switched Telephone Network Quality of Service Real-time Transport Protocol ServiceChange Switched Circuit Network Signalling Gateway Signalling System No. 7 Termination

This Recommendation uses the following abbreviations:

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Conventions

In this Recommendation, "shall" refers to a mandatory requirement, while "should" refers to a suggested but optional feature or procedure. The term "may" refers to an optional course of action without expressing a preference. 6 Connection model

The connection model for the protocol describes the logical entities, or objects, within the Media Gateway that can be controlled by the Media Gateway Controller. The main abstractions used in the connection model are terminations and contexts. A termination sources and/or sinks one or more streams. In a multimedia conference, a termination can be multimedia and sources or sinks multiple media streams. The media stream parameters, as well as bearer parameters are encapsulated within the termination. A context is an association between a collection of terminations. There is a special type of context, the NULL Context, which contains all terminations that are not present in any other context and therefore not associated to any other termination. For instance, in a decomposed access gateway, all idle lines are represented by terminations in the NULL Context. Following is a graphical depiction of these concepts. The diagram of Figure 1 gives several examples and is not meant to be an all-inclusive illustration. The asterisk box in each of the contexts represents the logical association of terminations implied by the context.

Figure 1/H.248.1 Example of H.248.1 connection model The example in Figure 2 shows an example of one way to accomplish a call-waiting scenario in a decomposed access gateway, illustrating the relocation of a termination between contexts. Terminations T1 and T2 belong to Context C1 in a two-way audio call. A second audio call is waiting for T1 from Termination T3. T3 is alone in Context C2. T1 accepts the call from T3, placing T2 on hold. This action results in T1 moving into Context C2, as shown in Figure 3.

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Figure 2/H.248.1 Example call waiting scenario/alerting applied to T1

Figure 3/H.248.1 Example call waiting scenario/answer by T1 6.1 Contexts

A context is an association between a number of terminations. The context describes the topology (who hears/sees whom) and the media mixing and/or switching parameters if more than two terminations are involved in the association. There is a special context called the NULL Context. It contains terminations that are not present in any other context and therefore not associated to any other termination. Terminations in the NULL Context can have their parameters examined or modified, and may have events detected on them. In general, an Add Command is used to add terminations to contexts. If the MGC does not specify an existing context to which the termination is to be added, the MG creates a new context. A termination may be removed from a context with a Subtract Command, and a termination may be moved from one context to another with a Move Command. A termination shall exist in only one context at a time.ITU-T Rec. H.248.1 (09/2005) 7

The maximum number of terminations in a context is a MG property. Media gateways that offer only point-to-point connectivity might allow at most two terminations per context. Media gateways that support multipoint conferences might allow three or more terminations per context. 6.1.1 Context attributes and descriptors The attributes of contexts are: ContextID. The Topology Descriptor (who hears/sees whom). The topology of a context describes the flow of media between the terminations within a context. In contrast, the Mode Property of a termination ("SendOnly"/"RecvOnly"/) describes the flow of the media at the egress/ingress of the media gateway. The priority is used for a context in order to provide the MG with information about a certain precedence handling for a context. The MGC can also use the priority to control autonomously the traffic precedence in the MG in a smooth way in certain situations (e.g., restart), when a lot of contexts must be handled simultaneously. Priority 0 is the lowest priority and a priority of 15 is the highest priority. An indicator for an emergency call is also provided to allow a preference handling in the MG. An indicator for an IEPS call is provided to allow the features and techniques of E.106 to be achieved. 6.1.2 A ContextAttribute Descriptor that enables extra context attributes to be defined by using the packages extension mechanism (see 7.1.19). Creating, deleting and modifying contexts

The protocol can be used to (implicitly) create contexts and modify the parameter values of existing contexts. The protocol has commands to add terminations to contexts, subtract them from contexts, and to move terminations between contexts. Contexts are deleted implicitly when the last remaining termination is subtracted or moved out. 6.2 Terminations

A termination is a logical entity on a MG that sources and/or sinks media and/or control streams. A termination is described by a number of characterizing properties, which are grouped in a set of descriptors that are included in commands. Terminations have unique identities (TerminationIDs), assigned by the MG at the time of their creation. Terminations representing physical entities have a semi-permanent existence. For example, a termination representing a TDM channel might exist for as long as it is provisioned in the gateway. Terminations representing ephemeral information flows, such as RTP flows, would usually exist only for the duration of their use. Ephemeral terminations are created by means of an Add Command. They are destroyed by means of a Subtract Command. In contrast, when a physical termination is Added to or Subtracted from a context, it is taken from or to the NULL Context, respectively. Terminations may have signals applied to them (see 7.1.11). Terminations may be programmed to detect events, the occurrence of which can trigger notification messages to the MGC, or action by the MG. Statistics may be accumulated on a termination. Statistics are reported to the MGC upon request (by means of the AuditValue Command, see 7.2.5) and when the termination ceases to exist or is returned to the NULL Context due to a Subtract Command. Multimedia gateways may process multiplexed media streams. For example, ITU-T Rec. H.221 describes a frame structure for multiple media streams multiplexed on a number of digital 64 kbit/s8 ITU-T Rec. H.248.1 (09/2005)

channels. Such a case is handled in the connection model in the following way. For every bearer channel that carries part of the multiplexed streams, there is a physical or ephemeral "bearer termination". The bearer terminations that source/sink the digital channels are connected to a separate termination called the "multiplexing termination". The multiplexing termination is an ephemeral termination representing a frame-oriented session. The Multiplex Descriptor for this termination describes the multiplex used (e.g., H.221 for an H.320 session) and indicates the order in which the contained digital channels are assembled into a frame. Multiplexing terminations may be cascades (e.g., H.226 multiplex of digital channels feeding into a H.223 multiplex supporting an H.324 session). The individual media streams carried in the session are described by Stream Descriptors on the multiplexing termination. These media streams can be associated with streams sourced/sunk by terminations in the context other than the bearer terminations supporting the multiplexing termination. Each bearer termination supports only a single data stream. These data streams do not appear explicitly as streams on the multiplexing termination and they are hidden from the rest of the context. Figures 4, 5, and 6 illustrate typical applications of the multiplexing termination and Multiplex Descriptor.

Figure 4/H.248.1 Multiplexed termination scenario Circuit-to-packet

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Figure 5/H.248.1 Multiplexed termination scenario Circuit-to-circuit

Figure 6/H.248.1 Multiplexed termination scenario Single-to-multiple terminations Unlike the multiplexing terminations described in the previous paragraph the multiplexed bearer termination, which represent multiplexed bearers such as ATM AAL Type 2 bearers, carry no media streams. They are present strictly for the purpose of modeling the creation and destruction of the actual bearer. When a new multiplexed bearer is to be created, an ephemeral termination is created in a context established for this purpose. When the termination is subtracted, the multiplexed bearer is destroyed. 6.2.1 Termination dynamics The protocol can be used to create new terminations and to modify property values of existing terminations. These modifications include the possibility of adding or removing events and/or signals. The termination properties, and events and signals are described in the ensuing subclauses. An MGC can only release/modify terminations and the resources that the termination represents which are in the NULL Context or which have been previously seized via e.g., the Add Command.

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6.2.2

TerminationIDs

Terminations are referenced by a TerminationID, which is an arbitrary schema chosen by the MG. TerminationIDs of physical terminations are provisioned in the Media Gateway. The TerminationIDs may be chosen to have structure. For instance, a TerminationID may consist of trunk group and a trunk within the group. A wildcarding mechanism using two types of wildcards can be used with TerminationIDs. The two wildcards are ALL and CHOOSE. The former is used to address multiple terminations at once, while the latter is used to indicate to a media gateway that it must select a termination satisfying the partially specified TerminationID. This allows, for instance, that a MGC instructs a MG to choose a circuit within a trunk group. TerminationIDs can also be specified in a list. The use of TerminationIDList is recommended for cases where a hierarchical TerminationID structure is not possible and it is not desired to send individual commands for each TerminationID. 6.2.3 Packages Different types of gateways may implement terminations that have widely differing characteristics. Variations in terminations are accommodated in the protocol by allowing terminations to have optional properties, events, signals and statistics implemented by MGs. In order to achieve MG/MGC interoperability, such options are grouped into packages, and typically a termination realizes a set of such packages. More information on definition of packages can be found in clause 12. An MGC can audit a termination to determine which packages it realizes. Properties, events, signals and statistics defined in packages, as well as parameters to them, are referenced by identifiers (IDs). Identifiers are scoped. For each package, PropertyIDs, EventIDs, SignalIDs, StatisticIDs and ParameterIDs have unique name spaces and the same identifier may be used in each of them. Two PropertyIDs in different packages may also have the same identifier, etc. To support a particular package the MG must recognize all properties, signals, events and statistics defined in a package. It must also support all signal and event parameters. If the functionality behind these properties, signals, events and statistics is not implemented, the MG shall not return a syntax error or unknown ID error for any of these elements but should return error 501 "Not implemented". The MG may support a subset of the values listed in a package for a particular property or parameter. If an unsupported value is specified by the MGC, the MG shall return error 501 "Not implemented". When packages are extended, the properties, events, signals and statistics defined in the base package can be referred to using either the extended package name or the base package name. For example, if Package A defines Event e1, and Package B extends Package A, then B/e1 is an event for a termination implementing Package B. By definition, the MG must also implement the base package, but it is optional to publish the base package as an allowed interface. If it does publish A, then A would be reported on the Packages Descriptor in AuditValue as well as B, and Event A/e1 would be available on a termination. If the MG does not publish A, then only B/e1 would be available. If published through AuditValue, A/e1 and B/e1 are the same event. For improved interoperability and backward compatibility, an MG may publish all packages supported by its terminations, including base packages from which extended packages are derived. An exception to this is in cases where the base packages are expressly defined as "Designed to be extended only".

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6.2.4

Termination properties and descriptors

Terminations have properties. The properties have unique PropertyIDs. Most properties have default values, which are explicitly defined in this protocol specification or in a package (see clause 12) or set by provisioning. If not provisioned otherwise, the properties in all descriptors except TerminationState and LocalControl default to empty/"no value" when a termination is first created or returned to the NULL Context. When a termination is first created or returned to the NULL Context, this state represents an "idle" line, trunk or other entity. The default contents of the two exceptions are described in 7.1.5 and 7.1.7. The provisioning of a property value in the MG will override any default value, be it supplied in this protocol specification or in a package. Therefore, if it is essential for the MGC to have full control over the property values of a termination, it should supply explicit values when adding the termination to a context. Alternatively, for a physical termination the MGC can determine any provisioned property values by auditing the termination while it is in the NULL Context. There are a number of common properties for terminations and properties specific to media streams. The common properties are also called the TerminationState properties. For each media stream, there are local properties and properties of the received and transmitted flows. Properties not included in the base protocol are defined in packages. These properties are referred to by a name consisting of the package name and a PropertyID. Most properties have default values described in the package description. Properties may be read-only or read/write. The possible values of a property may be audited, as can their current values. For properties that are read/write, the MGC can set their values. A property may be declared as "global" which has a single value shared by all terminations realizing the package. Related properties are grouped into descriptors for convenience. When a termination is added to a context, the value of its read/write properties can be set by including the appropriate descriptors as parameters to the Add Command. Similarly, a property of a termination in a context may have its value changed by the Modify Command. Properties may also have their values changed when a termination is moved from one context to another as a result of a Move Command. In some cases, descriptors are returned as output from a command. Setting properties on different terminations in the same context implicitly instructs the MG to perform certain functions. For example: if a G.711 codec is set on Termination A and a G.729 codec is set on Termination B, then the MG will activate a transcoding function as soon as a media flow is enabled between the two terminations (i.e., by setting the Mode Property to a state other than "Inactive" at each termination).NOTE To avoid unnecessary activation of MG resources, the MGC should set the Mode Property to "Inactive" for a given termination and stream until the properties to be used for that stream have been determined.

In general, if a descriptor is completely omitted from one of the aforementioned commands, the properties in that descriptor retain their prior values for the termination(s) upon which the command acts. On the other hand, if some read/write properties are omitted from a descriptor in a command (i.e., the descriptor is only partially specified), those properties will be reset to their default values for the termination(s) upon which the command acts, unless the package specifies other behaviour. For more details, see 7.1 dealing with the individual descriptors. The above behaviour applies equally to signals and events and their respective parameters. The provisioning of Events Descriptors would include the RequestID to use and any parameters of the included events. Any provisioning in the MG with respect to Events Descriptors should be duplicated in the MGC to avoid error responses to Notify Commands from the MG. The following table lists all of the possible descriptors and their use. Not all descriptors are legal as input or output parameters to every command.

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Descriptor name Modem Mux Media TerminationState Stream Local Remote LocalControl Events EventBuffer Signals Audit Packages DigitMap ServiceChange ObservedEvents Statistics Topology ContextAttribute Error

Description Identifies modem type and properties when applicable. (Note) Describes multiplex type for multimedia terminations (e.g., H.221, H.223, H.225.0) and terminations forming the input mux. A list of media stream specifications (see 7.1.4). Properties of a termination (which can be defined in packages) that are not stream specific. A list of Remote/Local/LocalControl Descriptors for a single stream. Contains properties that specify the media flows that the MG receives from the remote entity. Contains properties that specify the media flows that the MG sends to the remote entity. Contains properties (which can be defined in packages) that are of interest between the MG and the MGC. Describes events to be detected by the MG and what to do when an event is detected. Describes events to be detected by the MG when event buffering is active. Describes signals (see 7.1.11) applied to terminations. In Audit commands, identifies which information is desired. In AuditValue, returns a list of packages realized by the termination. Defines patterns against which sequences of a specified set of events are to be matched so they can be reported as a group rather than singly. In ServiceChange, what, why ServiceChange occurred, etc. In Notify or AuditValue, report of events observed. In Subtract and Audit, report of statistics kept on a termination or stream. Specifies flow directions between terminations in a context. Contains properties (which can be defined in packages) that affect the context as a whole. Contains an Error Code and optionally error text; it may occur in command replies and in Notify requests.

NOTE Modem Descriptor has been deprecated in ITU-T Rec. H.248.1 version 2 (05/2002).

6.2.5

Root Termination

Occasionally, a command must refer to the gateway as an entity in itself, rather than a termination within it. A special TerminationID, "Root" is reserved for this purpose. Packages may be defined on Root. Root thus may have properties, events, signals and statistics. Accordingly, the Root TerminationID may appear in: a Modify Command to change a property, send a signal or set an event; a Notify Command to report an event; an AuditValue Command to examine the values of properties and statistics implemented on Root; an AuditCapabilities Command to determine what properties of Root are implemented; a ServiceChange to declare the entire gateway in or out of service.

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Any other use of the Root TerminationID is an error. Error Code 410 ("Incorrect identifier") shall be returned in these cases. 6.3 Wildcarding principles

This clause specifies the behaviour for wildcarding ContextIDs and TerminationIDs that shall be applied to all commands. In processing these commands two forms of wildcarding must be considered: 1) Context wildcarding; 2) Termination wildcarding. For the purposes of the wildcarding procedures, a TerminationIDList consisting of more than one TerminationID is considered a wildcarded TerminationID. When executing a transaction that contains wildcarded contexts and optionally wildcarded terminations, all commands in the transaction are executed in order for a particular instance of ContextID before moving to a subsequent ContextID instance. In the case that there are multiple commands in a transaction, only when the TerminationID (wildcarded or specific) specified in the first command matches a specific instance of a ContextID are subsequent commands in the transaction executed. If a TerminationID (wildcarded or specific) of the subsequent command(s) in that transaction does not match the specific ContextID instance, then Error Code 431 ("No TerminationID matched a wildcard") is returned and processing of subsequent instances of the wildcard ContextID are stopped unless the command that generated the error is marked optional. The execution of particular wildcard combinations is discussed below. 6.3.1 ContextID specific with TerminationID wildcarded In the case where the ContextID is specific, when ALL is used in the TerminationID of a command, the effect is identical to repeating the command with each of the matching TerminationIDs. The use of ALL does not address the Root termination. Since each of these commands may generate a response, the size of the entire response may be large. Thus, if the wildcard matches more than one TerminationID in the context, all possible matches are attempted, with results reported for each one. If none of the terminations referenced by the wildcarded TerminationID are in the specific context, then Error Code 431 ("No TerminationID matched a wildcard") is returned. No errors are returned for individual terminations specified by the wildcarded TerminationID that are not in the specified context. For example: Assume that a gateway has four terminations: t1/1, t1/2, t2/1 and t2/2. Assume that Context 1 has t1/1 and t2/1 in it and that Context 2 has t1/2 and t2/2 in it. The command: Context=1{Command=t1/*{Descriptor/s}} returns: Context=1{Command=t1/1{Descriptor/s}} 6.3.2 ContextID wildcarded (ALL) with TerminationID specific In the case where the ContextID is wildcarded (i.e., ContextID = ALL) and the TerminationID is fully specified, the effect is identical to a command specifying the non-NULL context that contains the specified termination. Thus, a search must be made to find the context and only one instance of the command is executed. No errors are reported for contexts that do not contain the specified termination. If the termination is not contained in any (non-NULL) context, then Error Code 431 ("No TerminationID matched a wildcard") is returned. If there are no contexts other than NULL in existence, Error Code 411 ("The transaction refers to an unknown ContextID") is returned. Use of this form of action rather than one specifying the ContextID is discouraged but may be useful, for example in correcting conflicting state between MG and MGC.14 ITU-T Rec. H.248.1 (09/2005)

For example: Taking the above gateway configuration, the command: Context=*{Command=t1/1{Descriptor/s}} returns: Context=1{Command=t1/1{Descriptor/s}} 6.3.3 ContextID wildcarded (ALL) with TerminationID wildcarded In the case where the ContextID is wildcarded (i.e., ContextID = ALL) and the TerminationID is wildcarded, the effect is identical to repeating the command with each of the TerminationIDs matching the wildcard for each non-NULL context that contains one or more of those matching TerminationIDs. Thus if the wildcard matches more than one TerminationID in the specific instance of the wildcarded ContextID, all possible matches are attempted, with results reported for each one. No errors are reported for contexts that do not contain a termination matching the wildcarded TerminationID. No errors are returned for individual terminations specified in the wildcarded TerminationID that are not in a specific instance of the wildcarded ContextID. If there are no matches to the wildcarded ContextID and TerminationID, then Error Code 431 ("No TerminationID matched a wildcard") is returned. For example: Taking the above gateway configuration, the command: Context=*{Command=t1/*{Descriptor/s}} returns: Context=1{Command=t1/1{Descriptor/s}} Context=2 {Command=t1/2{Descriptor/s}} In the case that multiple commands are contained in a wildcarded TerminationID and/or wildcarded ContextID request, then if the first command does not match the first ContextID and TerminationID instance, then the subsequent command in the request will not be executed for that instance. 6.3.4 Wildcarded responses If individual responses are not required, a wildcard response may be requested. In such a case, a single response is generated, which contains the UNION of all of the individual responses which otherwise would have been generated, with duplicate values suppressed. For instance, given Termination Ta with Properties p1=a, p2=b and Termination Tb with Properties p2=c, p3=d, a UNION response would consist of a wildcarded TerminationID and the sequence of Properties p1=a, p2=b,c and p3=d. Wildcard responses may be particularly useful in the Audit commands. If a wildcard UNION response is used in conjunction with a wildcarded context, then a single response is sent with the UNION of all the individual terminations referenced by the TerminationID. The response would contain Context=ALL, a wildcarded TerminationID and the sequence of properties. If an error occurs during the execution of a wildcarded request that specifies a wildcarded response, special handling is required to provide useful information about the error(s) while still maintaining a modest sized response. When a wildcarded response is requested, all instances (as specified above) of the command shall be executed even if one or more result in errors, but later commands in the transaction will not be executed (unless optional was specified). Multiple command responses shall be returned for the command that encountered the error. The first command response shall be the normal wildcard response containing the UNION of responses for those commands that succeeded. If none of them succeeded, the UNION shall be empty. Additional command responses for each TransactionID that failed shall be returned with the appropriate Error Descriptor. For example, the command: Context=*{Command=t1/*{Descriptor/s}}

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Response to an error: Context=*{Command=t1/*{Union response descriptors}, Command=t1/3{Error=errorcode}} The encoding of the wildcarding mechanism is detailed in Annexes A and B. 7 Commands

The protocol provides commands for manipulating the logical entities of the protocol connection model, contexts and terminations. Commands provide control at the finest level of granularity supported by the protocol. For example, commands exist to add terminations to a context, modify terminations, subtract terminations from a context, and audit properties of contexts or terminations. Commands provide for complete control of the properties of contexts and terminations. This includes specifying which events a termination is to report, which signals/actions are to be applied to a termination and specifying the topology of a context (who hears/sees whom). Most commands are for the specific use of the Media Gateway Controller as command initiator in controlling Media Gateways as command responders. The exceptions are the Notify and ServiceChange Commands: Notify is sent from Media Gateway to Media Gateway Controller, and ServiceChange may be sent by either entity. Below is an overview of the commands; they are explained in more detail in 7.2. 1) Add: The Add Command adds a termination to a context. The Add Command on the first termination in a context is used to create a context. 2) Modify: The Modify Command modifies the properties, events and signals of a termination. 3) Subtract: The Subtract Command disconnects a termination from its context and returns statistics on the termination's participation in the context. The Subtract Command on the last termination in a context deletes the context. 4) Move: The Move Command atomically moves a termination to another context. 5) AuditValue: The AuditValue Command returns the current state of properties, events, signals and statistics of terminations. 6) AuditCapabilities: The AuditCapabilities Command returns all the possible values for termination properties, events and signals allowed by the Media Gateway. 7) Notify: The Notify Command allows the Media Gateway to inform the Media Gateway Controller of the occurrence of events in the Media Gateway. 8) ServiceChange: The ServiceChange Command allows the Media Gateway to notify the Media Gateway Controller that a termination or group of terminations is about to be taken out of service or has just been returned to service. ServiceChange is also used by the MG to announce its availability to a MGC (registration), and to notify the MGC of impending or completed restart of the MG. The MGC may announce a handover to the MG by sending it a ServiceChange Command. The MGC may also use ServiceChange to instruct the MG to take a termination or group of terminations in or out of service. These commands are detailed in 7.2.1 through 7.2.8. 7.1 Descriptors

The parameters to a command are termed descriptors. A descriptor consists of a name and a list of items. Some items may have values. Many commands share common descriptors. This subclause enumerates these descriptors. Descriptors may be returned as output from a command. In any such return of descriptor contents, an empty descriptor is represented by its name unaccompanied by any

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list. Parameters and parameter usage specific to a given command type are described in the subclause that describes the command. 7.1.1 Specifying parameters Command parameters are structured into a number of descriptors. In general, the text format of descriptors is DescriptorName={parm=value, parm=value}. Parameters may be fully specified, overspecified or underspecified: 1) Fully specified parameters have a single, unambiguous value that the command initiator is instructing the command responder to use for the specified parameter. 2) Underspecified parameters, using the CHOOSE value, allow the command responder to choose any value it can support. 3) Overspecified parameters have a list of potential values. The list order specifies the command initiator's order of preference of selection. The command responder chooses one value from the offered list and returns that value to the command initiator. If a required descriptor other than the Audit Descriptor is unspecified (i.e., entirely absent) from a command, the previous values set in that descriptor for that termination, if any, are retained. In commands other than Subtract, a missing Audit Descriptor is equivalent to an empty Audit Descriptor. The behaviour of the MG with respect to unspecified parameters within a descriptor varies with the descriptor concerned, as indicated in succeeding subclauses. Whenever a parameter is underspecified or overspecified, the descriptor containing the value chosen by the responder is included as output from the command. Each command specifies the TerminationID the command operates on. This TerminationID may be "wildcarded". When the TerminationID of a command is wildcarded, the effect shall be as if the command was repeated with each of the TerminationIDs matched. 7.1.2 Modem Descriptor The Modem Descriptor specifies the modem type and parameters, if any, required for use in e.g., H.324 and text conversation. The descriptor includes the following modem types: V.18, V.22, V.22 bis, V.32, V.32 bis, V.34, V.90, V.91, Synchronous ISDN, and allows for extensions. By default, no Modem Descriptor is present in a termination. Use of the Modem Descriptor is deprecated in ITU-T Rec. H.248.1 Version 2 (05/2002) and subsequent versions. This means that the Modem Descriptor shall not be included as part of transmitted content and, if received, shall either be ignored or processed at the option of the implementation. Modem type is to be specified as an attribute of data streams in the Local Descriptor and the Remote Descriptor. 7.1.3 Multiplex Descriptor In multimedia calls, a number of media streams are carried on a (possibly different) number of bearers. The Multiplex Descriptor associates the media and the bearers. The descriptor includes the multiplex type: H.221; H.223; H.226; V.76; N 64K; possible extensions,

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and a set of TerminationIDs representing the multiplexed bearers, in order. For example:Mux = H.221{MyT3/1/2, MyT3/2/13, MyT3/3/6, MyT3/21/22}

The N 64K multiplex type implements the N 64K service (e.g., as defined by Q.931 Information Transfer Rate or Q.763 Transmission Medium Requirement). On the context side, it supports a single stream of wideband data. When a bearer termination is added implicitly to a context as a result of the creation of an N 64K multiplexing termination, the Stream Descriptor for the bearer termination shall take on the same values as the Stream Descriptor defined for the multiplex termination, except that the bearer termination bandwidth shall be 64 kbit/s. 7.1.4 Media Descriptor The Media Descriptor specifies the parameters for all the media streams. These parameters are structured into two descriptors: a TerminationState Descriptor, which specifies the properties of a termination that are not stream dependent, and one or more Stream Descriptors each of which describes a single media stream. A stream is identified by a StreamID. The StreamID shall be in the range of 1 to 65535. The StreamID is used to link the streams in a context that belong together. Multiple streams exiting a termination shall be synchronized with each other. Within the Stream Descriptor, there are up to four subsidiary descriptors: LocalControl, Local, Remote and Statistics. The relationship between these descriptors is thus: Media DescriptorTerminationState Descriptor Stream Descriptor LocalControl Descriptor Local Descriptor Remote Descriptor Statistics Descriptor

As a convenience, the LocalControl, Local, Remote or Statistics Descriptors may be included in the Media Descriptor without an enclosing Stream Descriptor. In this case, the StreamID is assumed to be one. 7.1.5 TerminationState Descriptor The TerminationState Descriptor contains the ServiceStates Property, the EventBufferControl Property and properties of a termination (defined in packages) that are not stream specific. The ServiceStates Property describes the overall state of the termination (not stream specific). A termination can be in one of the following states: "Test", "OutOfService", or "InService". The "Test" state indicates that the termination is being tested. The state "OutOfService" indicates that the termination cannot be used for traffic. The state "InService" indicates that a termination can be used or is being used for normal traffic. "InService" is the default state. Values assigned to properties may be simple values (integer/string/enumeration) or may be underspecified, where more than one value is supplied and the MG may make a choice: Alternative Values: multiple values in a list, one of which must be selected; Ranges: minimum and maximum values, a value between min and max must be selected, boundary values included; Greater Than/Less Than: value must be greater/less than specified value; CHOOSE Wildcard: the MG chooses from the allowed values for the property. The EventBufferControl Property specifies whether events are buffered following detection of an event in the Events Descriptor, or processed immediately. See 7.1.9 for details.18 ITU-T Rec. H.248.1 (09/2005)

7.1.5.1

TerminationState Properties ServiceStates The value of this property indicates the current service state of the termination. Enumeration InService: The termination is in-service and functioning normally. OutOfService: The termination is out-of-service and not available for traffic. Test: The termination is undergoing testing.

7.1.5.1.1 ServiceStates Property Name: Description: Type: Possible values:

Default: Defined in: Characteristics: Property Name: Description: Type: Possible values:

InService TerminationState Read/Write EventBufferControl Specifies whether events are buffered following detection of an event in the Events Descriptor, or processed immediately. See 7.1.9. Enumeration LockStep: OFF: Events are buffered and processed per 7.1.9. Events are processed immediately.

7.1.5.1.2 EventBufferControl

Default: Defined in: Characteristics: 7.1.6

OFF TerminationState Read/Write

Stream Descriptor

A Stream Descriptor specifies the parameters of a single bidirectional stream. These parameters are structured into three descriptors: one that contains termination properties specific to a stream and one each for local and remote flows. The Stream Descriptor includes a StreamID which identifies the stream. Streams are created by specifying a new StreamID on one of the terminations in a context. A stream is deleted by setting empty Local and Remote Descriptors for the stream with ReserveGroup and ReserveValue in LocalControl set to "False" on all terminations in the context that previously supported that stream. StreamIDs are of local significance between MGC and MG and they are assigned by the MGC. Within a context, StreamID is a means by which to indicate which media flows are interconnected: streams with the same StreamID are connected. If a termination is moved from one context to another, the effect on the context to which the termination is moved is the same as in the case that a new termination were added with the same StreamIDs as the moved termination. 7.1.7 LocalControl Descriptor The LocalControl Descriptor contains the Mode Property, the ReserveGroup and ReserveValue Properties and properties of a termination (defined in packages) that are stream specific, and are of interest between the MG and the MGC. Values of properties may be specified as in 7.1.1.ITU-T Rec. H.248.1 (09/2005) 19

The allowed values for the Mode Property are "SendOnly", "RecvOnly", "SendRecv", "Inactive" and "LoopBack". "SendOnly", "RecvOnly" and "LoopBack" are with respect to the exterior of the context, so that, for example, a stream set to mode = "SendOnly" does not pass received media into the context. When a stream is set to "LoopBack" on a termination, media received (Local Descriptor) on the termination will be looped back to the sending side (Remote Descriptor) of the termination and no media is passed between that termination and other terminations in the context. The looped back media shall be sent according to the Remote Descriptor. The default value for the Mode Property is "Inactive". Signals and events are not affected by the Mode Property. The LocalControl Mode Property takes precedence over any mode specified in the Local and Remote Descriptors. The boolean-valued Reserve Properties, ReserveValue and ReserveGroup, of a termination indicate what the MG is expected to do when it receives a Local and/or Remote Descriptor. If the value of a Reserve Property is "True", the MG shall reserve resources for all alternatives specified in the Local and/or Remote Descriptors for which it currently has resources available. It shall respond with the alternatives for which it reserves resources. If it cannot support any of the alternatives, it shall respond with a reply to the MGC that contains empty Local and/or Remote Descriptors. If media begins to flow while more than a single alternative is reserved, media packets may be sent or received on any of the alternatives and must be processed, although only a single alternative may be active at any given time. If the value of a Reserve Property is False, the MG shall choose one of the alternatives specified in the Local Descriptor (if present) and one of the alternatives specified in the Remote Descriptor (if present). If the MG has not yet reserved resources to support the selected alternative, it shall reserve the resources. If, on the other hand, it already reserved resources for the termination addressed (because of a prior exchange with ReserveValue and/or ReserveGroup equal to "True"), it shall release any excess resources it reserved previously. Finally, the MG shall send a reply to the MGC containing the alternatives for the Local and/or Remote Descriptor that it selected. If the MG does not have sufficient resources to support any of the alternatives specified, it shall respond with Error Code 510 ("Insufficient resources"). The default value of ReserveValue and ReserveGroup is "False". More information on the use of the two Reserve Properties is provided in 7.1.8. A new setting of the LocalControl Descriptor completely replaces the previous setting of that descriptor in the MG. Thus, to retain information from the previous setting, the MGC must include that information in the new setting. If the MGC wishes to delete some information from the existing descriptor, it merely resends the descriptor (in a Modify Command) with the unwanted information stripped out.NOTE The Mode Property is also known as "StreamMode" in the encoding definitions in Annexes A and B. These terms are interchangeable within H.248.

7.1.7.1

LocalControl Properties StreamMode The value of this property indicates the current service state of the termination. Enumeration

7.1.7.1.1 Mode Property Name: Description: Type:

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Possible values: Inactive: SendOnly: RecvOnly: SendRecv: LoopBack: Default: Defined in: Characteristics: Property Name: Description: Inactive LocalControl Read/Write ReserveGroup Specifies whether the MG should reserve the resources to support a single media group or as many media groups as it can, as they are defined in the Local and Remote Descriptors. See 7.1.8. The termination does not pass any media for the stream. The termination passes media for the stream from the interior to the exterior of the context. The termination passes media for the stream from the exterior to the interior of the context. The termination passes media for the stream both into and out of the context. The termination loops received media for the stream back to the sender.

7.1.7.1.2 ReserveGroup

NOTE The term "media group" designates the content of the ASN.1 production "PropertyGroup" (see Annex A) in the binary encoding, or an individual SDP session description in the text encoding.

Type: Possible values:

Boolean True: False: The MG is to reserve all possible media groups indicated in the Local and Remote Descriptors. The MG is to reserve a single media group from each of the Local and the Remote Descriptors according to the policies described in 7.1.8.

Default: Defined in: Characteristics: Property Name: Description:

False LocalControl Read/Write ReserveValue Specifies whether the MG should reserve the resources to support a single set of property values (e.g., a single codec and its associated attributes) or as many such sets as it can, as they are defined in the Local and Remote Descriptors. See 7.1.8. Boolean True: The MG is to reserve resources to serve as many as possible of the sets of property values indicated in the selected media group (if ReserveGroup is False) or in each media group (if ReserveGroup is True) in the Local and Remote Descriptors.

7.1.7.1.3 ReserveValue

Type: Possible values:

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False:

The MG is to reserve a single set of property values from those indicated in the selected media group (if ReserveGroup is False) or in each media group (if ReserveGroup is True) in the Local and Remote Descriptors.

Default: Defined in: Characteristics: 7.1.8

False LocalControl Read/Write

Local and Remote Descriptors

The MGC uses Local and Remote Descriptors to reserve and commit MG resources for media decoding and encoding for the given stream(s) and termination to which they apply. The MG includes these descriptors in its response to indicate what it is actually prepared to support. The MG shall include additional properties and their values in its response if these properties are mandatory yet not present in the requests made by the MGC (e.g., by specifying detailed video encoding parameters where the MGC only specified the payload type). To avoid ambiguity when requesting the MG to reserve and commit resources, the MGC should supply as much information as needed when using underspecification (i.e., CHOOSE) so that the MG can make an unambiguous selection. For example when using CHOOSE without specifying the required application type (e.g., "media name" in case of SDP encoding), further information may be needed (e.g., attribute lines in case of SDP encoding). Local refers to the media received by the MG and Remote refers to the media sent by the MG. When text encoding the protocol, the descriptors consist of session descriptions as defined in SDP (RFC 2327). In session descriptions sent from the MGC to the MG, the following exceptions to the syntax of RFC 2327 are allowed: the "s = ", "t = " and "o = " lines are optional; the use of CHOOSE is allowed in place of a single parameter value; and the use of alternatives is allowed in place of a single parameter value. A Stream Descriptor specifies a single bidirectional media stream and so a single session description must not include more than one media description ("m = " line). A Stream Descriptor may contain additional session descriptions as alternatives. Each media stream for a termination must appear in distinct Stream Descriptors. When multiple session descriptions are provided in one descriptor, the "v = " lines are required as delimiters; otherwise they are optional in session descriptions sent to the MG. Implementations shall accept session descriptions that are fully conformant to RFC 2327 according to the above restrictions. When binary encoding the protocol, the descriptor consists of groups of properties (tag-value pairs) as specified in Annex C. Each such group may contain the parameters of a session description. Below, the semantics of the Local and Remote Descriptors are specified in detail. The specification consists of two parts. The first part specifies the interpretation of the contents of the descriptor. The second part specifies the actions the MG must take upon receiving the Local and Remote Descriptors. The actions to be taken by the MG depend on the values of the ReserveValue and ReserveGroup Properties of the LocalControl Descriptor. Either the Local or the Remote Descriptor or both may be: unspecified (i.e., absent); empty; underspecified through use of CHOOSE in a property value; fully specified; or

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overspecified through presentation of multiple groups of properties and possibly multiple property values in one or more of these groups.

Where the descriptors have been passed from the MGC to the MG, they are interpreted according to the rules given in 7.1.1, with the following additional comments for clarification: a) An unspecified Local or Remote Descriptor is considered to be a missing mandatory parameter. It requires the MG to use whatever was last specified for that descriptor. It is possible that there was no previously specified value, in which case the descriptor concerned is ignored in further processing of the command. b) An empty Local (Remote) Descriptor in a message from the MGC signifies a request to release any resources reserved for the media flow received (sent). c) If multiple groups of properties are present in a Local or Remote Descriptor or multiple values within a group, the order of preference is descending. d) Underspecified or overspecified properties within a group of properties sent by the MGC are requests for the MG to choose one or more values which it can support for each of those properties. In case of an overspecified property, the list of values is in descending order of preference. Subject to the above rules, subsequent action depends on the values of the ReserveValue and ReserveGroup Properties in LocalControl. If ReserveGroup is "True", the MG reserves the resources required to support as many as possible of the requested property group alternatives that it can currently support. If ReserveValue is "True", the MG reserves the resources required to support as many as possible of the requested property value alternatives that it can currently support.NOTE If a Local or Remote Descriptor contains multiple groups of properties, and ReserveGroup is "True", then the MG is requested to reserve resources so that it can decode or encode the media stream according to any of the alternatives. For instance, if the Local Descriptor contains two groups of properties, one specifying packetized G.711 A-law audio and the other G.723.1 audio, the MG reserves resources so that it can decode one audio stream encoded in either G.711 A-law format or G.723.1 format. The MG does not have to reserve resources to decode two audio streams simultaneously, one encoded in G.711 A-law and one in G.723.1. The intention for the use of ReserveValue is analogous.

If ReserveGroup is "True" or ReserveValue is "True", then the following rules apply: If the MG has insufficient resources to support all alternatives requested by the MGC, and the MGC requested resources in both Local and Remote, the MG should reserve resources to support at least one alternative each within Local and Remote. If the MG has insufficient resources to support at least one alternative within a Local (Remote) Descriptor received from the MGC, it shall return an empty Local (Remote) in response. In its response to the MGC, when the MGC included Local and Remote Descriptors, the MG shall include Local and Remote Descriptors for all groups of properties and property values it reserved resources for. If the MG is incapable of supporting at least one of the alternatives within the Local (Remote) Descriptor received from the MGC, it shall return an empty Local (Remote) Descriptor. If the Mode Property of the LocalControl Descriptor is "RecvOnly", "SendRecv", or "LoopBack", the MG must be prepared to receive media encoded according to any of the alternatives included in its response to the MGC. If ReserveGroup is "False" and ReserveValue is "False", then the MG should apply the following rules to resolve Local and Remote to a single alternative each: The MG chooses the first alternative in Local for which it is able to support at least one alternative in Remote.ITU-T Rec. H.248.1 (09/2005) 23

If the MG is unable to support at least one Local and one Remote alternative, it returns Error Code 510 ("Insufficient resources"). The MG returns its selected alternative in each of Local and Remote.

A new setting of a Local or Remote Descriptor completely replaces the previous setting of that descriptor in the MG. Thus, to retain information from the previous setting, the MGC must include that information in the new setting. If the MGC wishes to delete some information from the existing descriptor, it merely resends the descriptor (in a Modify Command) with the unwanted information stripped out. 7.1.9 Events Descriptor The Events Descriptor parameter contains a RequestID and a list of events that the Media Gateway is requested to detect and report. The RequestID is used to correlate the request with the notifications that it may trigger. Requested events include, for example, fax tones, continuity test results, and on-hook and off-hook transitions. The RequestID is omitted if the Events Descriptor is empty (i.e., no events are specified). Each event in the descriptor contains the event name, an optional StreamID, an optional KeepActive flag, an optional NotifyBehaviour flag, an optional ResetEventsDescriptor flag and optional parameters. The event name consists of a PackageID (where the event is defined) and an EventID. The ALL wildcard may be used for the EventID, indicating that all events from the specified package have to be detected. The default StreamID is 0, indicating that the event to be detected is not related to a particular media stream. Events can have parameters. This allows a single event description to have some variation in meaning without creating large numbers of individual events. Further event parameters are defined in the package. If a DigitMap completion event is present or implied in the Events Descriptor, the EventDM Parameter is used to carry either the name or the value of the associated DigitMap. See 7.1.14 for further details. When an event is processed against the contents of an active Events Descriptor and found to be present in that descriptor ("recognized"), the default action of the MG is to send a Notify Command to the MGC. Notification may be deferred if the event is absorbed into the current dial string of an active DigitMap (see 7.1.14). The sending of a Notify Command may be influenced by the NotifyBehaviour flag. Moreover, event recognition may cause currently active signals to stop, or may cause the current Events and/or Signals Descriptor to be replaced, as described at the end of this subclause. Unless the Events Descriptor is replaced by another Events Descriptor, it remains active after an event has been recognized. If the value of the EventBufferControl Property equals "LockStep", following detection of such an event, normal handling of events is suspended. Any event which is subsequently detected and occurs in the EventBuffer Descriptor is added to the end of the EventBuffer (a FIFO queue), along with the time that it was detected. The MG shall wait for a new Events Descriptor to be loaded. A new Events Descriptor can be loaded either as the result of receiving a command with a new Events Descriptor, or by activating an embedded Events Descriptor. If EventBufferControl equals "Off", the MG continues processing based on the active Events Descriptor. In the case of an embedded Events Descriptor being activated, the MG continues event processing based on the newly activated Events Descriptor.NOTE 1 For purposes of EventBuffer handling, activation of an embedded Events Descriptor is equivalent to receipt of a new Events Descriptor.

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When the MG receives a command with a new Events Descriptor, one or more events may have been buffered in the EventBuffer in the MG. The value of EventBufferControl, then determines how the MG treats such buffered events. Case 1 If EventBufferControl equals "LockStep" and the MG receives a new Events Descriptor, it will check the FIFO EventBuffer and take the following actions: 1) If the EventBuffer is empty, the MG waits for detection of events based on the new Events Descriptor. 2) If the EventBuffer is non-empty, the MG processes the FIFO queue starting with the first event: a) If the event in the queue is in the events listed in the new Events Descriptor, the MG acts on the event and removes the event from the EventBuffer. The time stamp of the Notify shall be the time the event was actually detected. The MG then waits for a new Events Descriptor. While waiting for a new Events Descriptor, any events detected that appear in the EventBuffer Descriptor will be placed in the EventBuffer. When a new Events Descriptor is received, the event processing will repeat from step 1). b) If the event is not in the new Events Descriptor, the MG shall discard the event and repeat from step 1). Case 2 If EventBufferControl equals "Off" and the MG receives a new Events Descriptor, it processes new events with the new Events Descriptor. If the MG receives a command instructing it to set the value of EventBufferControl to "Off", all events in the EventBuffer shall be discarded. The MG may report several events in a single transaction as long as this does not unnecessarily delay the reporting of individual events. For procedures regarding transmitting the Notify Command, refer to the appropriate annex or H.248.x Recommendation for specific transport considerations. The default value of EventBufferControl is "Off".NOTE 2 Since the EventBufferControl Property is in the TerminationState Descriptor, the MG might receive a command that changes the EventBufferControl Property and does not include an Events Descriptor.

Normally, recognition of an event shall cause any active signals to stop. When KeepActive is specified in the event, the MG shall not interrupt any signals active on the termination on which the event is detected. The NotifyBehaviour flag may be used to indicate that the Notify Command is: sent immediately (NotifyImmediate: this is the default); never sent (NeverNotify); or regulated (i.e., sent or suppressed) according to the MGC load (RegulatedNotify). See E.15 for more details on the use of NotifyBehaviour. When used with DigitMaps the notify behaviour occurs when the active DigitMap is completed. The Regulated Notify may have an alternate regulated embedded Events or Signals Descriptor associated with it. If a notification is regulated (i.e., suppressed), then this alternate regulated embedded descriptor shall be activated. If the Notify is not regulated, then the original embedded descriptor is triggered. If NotifyImmediate or NeverNotify is set, then any original embedded descriptor is triggered on detection of the event. The result of encountering the ResetEventDescriptor flag set against an event depends on whether or not the Events Descriptor containing the event is an embedded Events Descriptor. In the case ofITU-T Rec. H.248.1 (09/2005) 25

an embedded Events Descriptor the ResetEventsDescriptor flag causes the Events Descriptor for that termination to be reset to its state prior to when the embedded descriptor was activated (i.e., the last Events Descriptor explicitly set by a Modify Command or, if there has been no Modify Command since the termination was last reset by being put into the NULL Context, the MG-provisioned Events Descriptor). In the case of a non-embedded Events Descriptor the ResetEventsDescriptor flag causes the active Events Descriptor for that termination to be reset by re-activating any DigitMap completion event(s) that have been matched and deactivated. The ResetEventsDescriptor flag shall be set on physical terminations only. The ResetEventsDescriptor flag shall be acted on when the termination is in the NULL Context. If the ResetEventsDescriptor flag is encountered when the termination is out of the NULL Context, then it shall have no effect. An event can include an embedded Signals Descriptor and/or an embedded Events Descriptor which, if present, replaces the current Signals/Events Descriptor when the event is recognized. It is possible, for example, to specify that the dial-tone signal be generated when an off-hook event is recognized, or that the dial-tone signal be stopped when a digit is recognized. A media gateway controller shall not send Events Descriptors with an event both marked KeepActive and containing an embedded Signals Descriptor. Only one level of embedding is permitted. An embedded Events Descriptor shall not contain another embedded Events Descriptor; an embedded Events Descriptor may contain an embedde